Electroplating process



Patented June 3, 1930 UNITED STATES PATENT OFFICE i RALPH J. WIRSHINGAND HENRY R. FAAS, OF DETROIT, MICHIGAN, ASSIGNORS TO GENERAL MOTORSRESEARCH CORPORATION, OF DETROIT, MICHIGAN, A CORPORA- TION OF DELAWAREELECTROPLATING PROCESS No Drawing.

The invention relates to electroplating and has particular reference tothe electrodeposition of nickel and chromium. It has been customary todeposit chromium upon nickel in order to produce a combined coating ofhigh protective efficiency. Upon nickel deposits as hitherto produced,however, it has been difiicult to apply a chromium deposit of more thana very limited thickness without causing the combined coating to peeloff or loosen from the metal body beneath. In fact, when nickel isdeposited by the usual methods of plating that metal, a subsequentapplication of chromium plating has been limited practically to thatobtainable in about five minutes plating.

We have found, however, that by use of a hot plating bath for depositionof the nickel a much softer and a much more adherent coating of nickelmay be obtained. The softer deposit materially facilitates the operationof bufling, and the greater adhesion of the nickel layer enables a.greatly increased thickness of chromium to be applied.

In the attempt to use the usual nickel sulphate bath at the elevatedtemperature at which we prefer to operate it is found that pitting ofthe nickel deposit occurs. The discovery has been made, however, that abath containing nickel acetate is capable of depositing nickel at a muchhigher temperature than a nickel sulphate bath without the occurrence ofpitting. In fact, the use of a low temperature with a nickel acetatebath seems to promote pitting whereas the high temperature operationinhibits pitting. Furthermore, the use of the nickel acetate bath at ahigh temperature enables a much higher current density to be used thanhas been found practicable with nickel sulphate baths thus facilitatinga material increase in the rate of deposit of the metal.

In practice we have found that 200 grams nickel acetate, and 15 gramssodium chloride, per liter of water will provide a satisfactory bath. Itwill be understood, of course, that a considerable range of proportionsis possible, for example, the sodium chloride may vary from 5-15 gramswithout materially affecting the results.

Serial No. 160,310.

The nickel acetate may be added to the bath directly or it may beproduced in the bath, as, for example, by reaction between acetic acidand nickel carbonate or basic carbonate.

The temperatures employed vary over a considable range but should beabove approximately 100 F. and the preferred range may be given asbetween 140 and 160 F.

The current density may be made quite high compared with that usual withother nickel baths. Best results have been obtained with densities of 15to 100 amperes per square foot at the cathode although densities as highas 500 amperes per sq. ft. have given good results. Nickel anodes areused.

In the plating of nickel or ferrous metals it is customary to first coatthe base metal with copper. When this procedure is followed we havefound it preferable to plate the copper from a copper cyanide bath,thereby decreasing the occurrence of rust stimulating salts in thecoating. It has been found desirable also to deposit the copper from ahot-solution, good results having been obtained with the temperature ofthe copper bath maintained above 150 F.

When it is desired to deposit chromium on the nickel, a chromium platingbath of ordinary character may be used, for example, thatof the typeknown as Sargents solution, or a bath containing approximately 200 gramsof chromic acid and 3 grams chromium sulphate per liter.

Proceeding as described above, we have found that thick deposits ofchromium may be easily applied over nickel and that these de posits arevery smooth and brilliant and the coating adheres strongly to the basemetal.

Modifications may, of course, be made by those skilled in the artwithout departing from the invention and therefore we do not Wish to berestricted to the details herein set forth except as required by thelanguage'of the appended claims in view of the prior art.

We claim:

1. The process of electrolytically depositing nickel comprising passingan electric current through a bath containing as its principal solutenickel acetate and including the maintenance of the bath duringelectrodeposition at a temperature between the approximate limits of 100to 160 F. J

2. The process of electrolytically depositing nickel comprising passingan electric current through a bath containing as its principal solutenickel acetate, including the main- 'tenance of the bath at atemperature of approximately to F.

3. The process as set forth in claim' 2 including the use of a currentdensity at the cathode of 15 to 100 amperes per square foot.

tures.

RALPH J. WIRSHING. HENRY R. FAAS.

In testimony whereof we aflix our signa-

